LA500A opto comp MAY 2021 BUILD THREAD 500/51X

[rohanz]

Just double checked, yeah im not sure how its happening but it is 4-5 db less in bypass. when you say comp alignment do you mean the calibration?

[Joe Malone]

Just double checked, yeah im not sure how its happening but it is 4-5 db less in bypass. when you say comp alignment do you mean the calibration?

Yes calibration?

Best to send me clear in focus well lit top and bottom photos of the pcbs to check over.

[rohanz]

yes the calibration went fine! only thing is the multimeter i have has a precision till 1.2 only so it might not be extremely accurate. i managed to solve the bypass issue, so now its just the meter getting stuck on the left. i will add the pcb pictures soon! btw when i say stuck on the left, i mean it moves as per normal but only if it moves really fast to the left it goes beyond the point of the 20 on the meter it kind of gets caught there. it needs a little tap or setting the meter to something else to get unstuck.

[Joe Malone]

yes the calibration went fine! only thing is the multimeter i have has a precision till 1.2 only so it might not be extremely accurate. i managed to solve the bypass issue, so now its just the meter getting stuck on the left. i will add the pcb pictures soon! btw when i say stuck on the left, i mean it moves as per normal but only if it moves really fast to the left it goes beyond the point of the 20 on the meter it kind of gets caught there. it needs a little tap or setting the meter to something else to get unstuck.

OK sounds mechanical in the meter. First things to try is adjusting the front screw on the meter that sets -20. With the comp off move the needle slightly up and then back to -20 as this will show the meter is still in the pivots properly. Also undoing the 4 meter bolts and doing them up again can remove mechanical stress in the meter frame. If that doesn't work the meter sometimes when the needle has pinned hard in GR below -20 it can bend the internal brass rest pin to an angle where it sticks to it.

[philly]

quick question...
just about to calibrate my first la500 build
if it's hooked up shouldn't the vu be illuminated?
the led's light up when i pull the pots...
it passes audio..tho vu doesnt respond...and whether its compressed or not i don't know for the time being.....
on meter switch set to vu the needle is hard left.. on gr its hard right... like off the scale...which i put down to the trim pots not being set properly?
just wondering why the meter isn't illuminated for time being
cheers

[Joe Malone]

quick question...
just about to calibrate my first la500 build
if it's hooked up shouldn't the vu be illuminated?
the led's light up when i pull the pots...
it passes audio..tho vu doesnt respond...and whether its compressed or not i don't know for the time being.....
on meter switch set to vu the needle is hard left.. on gr its hard right... like off the scale...which i put down to the trim pots not being set properly?
just wondering why the meter isn't illuminated for time being
cheers

The vu meter lights only in VU or GR position. In off the vu meter light is off to show it is out of the circuit.

Make sure you have the outside terminals of the meter and all switch solder pads soldered correctly for the led to work.

With the threshold and makeup fully CCW and switched to VU with no input the meter should not move and show -20 like when comp off. GR will show off the scale until adjusted.

[Joe Malone]

quick question...
just about to calibrate my first la500 build
if it's hooked up shouldn't the vu be illuminated?
the led's light up when i pull the pots...
it passes audio..tho vu doesnt respond...and whether its compressed or not i don't know for the time being.....
on meter switch set to vu the needle is hard left.. on gr its hard right... like off the scale...which i put down to the trim pots not being set properly?
just wondering why the meter isn't illuminated for time being
cheers

The vu meter lights only in VU or GR position. In off the vu meter light is off to show it is out of the circuit.

Make sure you have the outside terminals of the meter and all switch solder pads soldered correctly for the led to work. Also that you do not have a short between any meter solder pads

If the led has gone open circuit the comp will be stuck in off. If the led has gone short circuit the comp will switch in on VU and GR but no light.

With the threshold and makeup fully CCW and switched to VU with no input the meter should not move and show -20 like when comp off. GR will show off the scale until adjusted.

[philly]

quick question...
just about to calibrate my first la500 build
if it's hooked up shouldn't the vu be illuminated?
the led's light up when i pull the pots...
it passes audio..tho vu doesnt respond...and whether its compressed or not i don't know for the time being.....
on meter switch set to vu the needle is hard left.. on gr its hard right... like off the scale...which i put down to the trim pots not being set properly?
just wondering why the meter isn't illuminated for time being
cheers

The vu meter lights only in VU or GR position. In off the vu meter light is off to show it is out of the circuit.

Make sure you have the outside terminals of the meter and all switch solder pads soldered correctly for the led to work. Also that you do not have a short between any meter solder pads

If the led has gone open circuit the comp will be stuck in off. If the led has gone short circuit the comp will switch in on VU and GR but no light.

With the threshold and makeup fully CCW and switched to VU with no input the meter should not move and show -20 like when comp off. GR will show off the scale until adjusted.

thanks Joe !!

I re-flowed all toggle switch points and still getting the same issue
i have noticed tho that if i put slight finger pressure on the vu toggle solder points i get a faint meter light and the needle moves to the right. the amount it moves depends on the pressure i exert?... this happens where toggle is on gr, off or vu
i'm hoping to disconnect the pcb from housing bracket tomorrow to have a better look
one thing im a bit worried about is the optos... there seems to be some different solder points and silk graphics depending on board version according to pics i've seen on this thread
would you be so kind as to have a look at pic of mine and confirm if i've used correct points for my pcb?



thanks again

[Joe Malone]

I re-flowed all toggle switch points and still getting the same issue
i have noticed tho that if i put slight finger pressure on the vu toggle solder points i get a faint meter light and the needle moves to the right. the amount it moves depends on the pressure i exert?... this happens where toggle is on gr, off or vu
i'm hoping to disconnect the pcb from housing bracket tomorrow to have a better look
one thing im a bit worried about is the optos... there seems to be some different solder points and silk graphics depending on board version according to pics i've seen on this thread
would you be so kind as to have a look at pic of mine and confirm if i've used correct points for my pcb?



thanks again

Sounds like your finger resistance is lighting the vu meter since it does it in all 3 positions. Need clear in focus photos of the BIO500 Pcb top and bottom to check the relay is the correct way around. Also to check it is fully soldered as well the rest of the pcb. Attach photos as attachments as it makes it easier and they will not disappear in the future.

Both sets of holes are linked to closest hole next to it so either is fine to use

The photo is to small and blurry but are the optos in reversed direction ?. Dot needs to be were dots are on the pcb. You can use either set of holes so that fine. Need clear in focus well lit large photos to be able to help

Photo is very hard to see but text looks correct way around and I cannot see dot so I presume it is on the otherside next to the dot on the pcb?

[rack11]

Hi Joe,

I soldered my optos on the inner holes as highlighted in green. Is this going to be an issue?

optoSpots.jpg

Thank you.

[Joe Malone]

Hi Joe,

I soldered my optos on the inner holes as highlighted in green. Is this going to be an issue?
optoSpots.jpg

Thank you.

Both sets of holes are linked to closest hole next to it so either is fine to use

[rack11]

Hi Joe,

I think the instruction for the sockets is very vague. I couldn't figure out what you meant with it, and it is hard to tell in your pictures whether you soldered it.
Fit 6 x 1mm sockets for 99v opamp. Do NOT press the sockets in. Just let them sit in the holes. Use a piece of cardboard to hold them in while turning the PCB over.

For those like me confused, I eventually soldered mine at the end, but I should have soldered it at the start as the board becomes tighter with parts installed. The cardboard thing, I didn't know what you meant. I used masking tape to keep the sockets pushed up against the PCB. At first I was concerned that it may be too low that the opamps will hit the resistors, but the legs on the opamps are tall. Not sure if the bottom sockets touch the bottom plate and may short it. I will check when I try calibrating.

Also, regarding the yellow transformer, how tight are you meant to screw the mounting screws? I am concerned if I keep on turning it, it will squeeze the transformer and deform it. Are they windings in there, or is there a shell to protect it from being overscrewed and compressed?

Thank you.

[Joe Malone]

Hi Joe,

I think the instruction for the sockets is very vague. I couldn't figure out what you meant with it, and it is hard to tell in your pictures whether you soldered it.
Fit 6 x 1mm sockets for 99v opamp. Do NOT press the sockets in. Just let them sit in the holes. Use a piece of cardboard to hold them in while turning the PCB over.

For those like me confused, I eventually soldered mine at the end, but I should have soldered it at the start as the board becomes tighter with parts installed. The cardboard thing, I didn't know what you meant. I used masking tape to keep the sockets pushed up against the PCB. At first I was concerned that it may be too low that the opamps will hit the resistors, but the legs on the opamps are tall. Not sure if the bottom sockets touch the bottom plate and may short it. I will check when I try calibrating.

Yes 1mm sockets should be fitted first. They should just go into the pcb as far as they will go which is when they hit the wider shoulder on the socket.

Also, regarding the yellow transformer, how tight are you meant to screw the mounting screws? I am concerned if I keep on turning it, it will squeeze the transformer and deform it. Are they windings in there, or is there a shell to protect it from being overscrewed and compressed?

Just tighten until the transformer laminates are packed tight and the side tape wrinkles. If you are stripping the Philips head screw then you are going to tight.

[rack11]

Just checked, the opamps socket bottoms have plenty of clearance when on the metal chassis, so it was not a concern.

Calibration
Sine level
I used a Multimeter to get the sine tone level of +4 from the output XLR of the lunchbox with the unit installed, but I used XLR pin 1 and 2, but your instructions states pin 2 and 3? I do not get enough voltage using 2 and 3, the readings I get are mini-volts and not normal volts, unlike with pin 1 and 2 where its volts? Is this right?

Balance Trimpot
I followed the instructions of turning the threshold knob until 5 on the VU, then flipping the Meter switch between GR and VU, to see if the VU readings match and if not, turn the Balance trimpot. When you turn the trimpot both VU and GR will change simultaneously, in opposite direction, so you switch back and forth and adjust the trimpot until they both meet and match.

I started at 5 on the VU meters and eventually when turning the balance trimpot, both VU and GR meter mode meets, and for my unit, it was about 3 on the VU as shown below. Is this typically what you should get Joe?

balanceTrim.jpg

Does the VU/GR meeting value change, depending on whether you have fed it the right signal? Like if I did not adjust the previous Zero calibration for the VU properly, would the meeting reading be different than my 3?

Test
I finished the calibration and did a quick test feeding it recorded vocals, bass and a mix and it seems to behave as it should.

[Joe Malone]

Just checked, the opamps socket bottoms have plenty of clearance when on the metal chassis, so it was not a concern.

Calibration
Sine level
I used a Multimeter to get the sine tone level of +4 from the output XLR of the lunchbox with the unit installed, but I used XLR pin 1 and 2, but your instructions states pin 2 and 3? I do not get enough voltage using 2 and 3, the readings I get are mini-volts and not normal volts, unlike with pin 1 and 2 where its volts? Is this right?

XLR 2 & pin 3 is the balanced out and is the only correct pins to measure the +4dBu (1.23vac) Pin 1 is ground and pin 2 one side of the floating transformer output so there should be almost no volts. So I think you have this the wrong way around and have used pin 2 & 3. Remember pin 1 is on the opposite side in chassis male and female XLRs

Balance Trimpot
I followed the instructions of turning the threshold knob until 5 on the VU, then flipping the Meter switch between GR and VU, to see if the VU readings match and if not, turn the Balance trimpot. When you turn the trimpot both VU and GR will change simultaneously, in opposite direction, so you switch back and forth and adjust the trimpot until they both meet and match.

Yes correct and when the meet readjust threshold to check they are correct at -5dB

I started at 5 on the VU meters and eventually when turning the balance trimpot, both VU and GR meter mode meets, and for my unit, it was about 3 on the VU as shown below. Is this typically what you should get Joe?
balanceTrim.jpg

Will usually be within +/-1dB of -5dB

Does the VU/GR meeting value change, depending on whether you have fed it the right signal? Like if I did not adjust the previous Zero calibration for the VU properly, would the meeting reading be different than my 3?

If you do not set +4dBu using the correct output pins then the 0VU will be wrong and all of the calibration will be wrong.